Journeyman Plumbers Exam Drainage, Waste, and Vent Systems 5 — Questions and Answers
Question 1: Under the IPC, what is the maximum number of fixture units permitted on a 3-inch horizontal branch drain sloped at 1/4 inch per foot?
- 10 DFUs
- 20 DFUs (Correct answer)
- 30 DFUs
- 42 DFUs
Correct answer: 20 DFUs
A 3-inch horizontal branch at 1/4-inch-per-foot slope can carry a maximum of 20 drainage fixture units per IPC Table 710.1(2).
Question 2: Which of the following best describes back-pressure (positive pressure) in a drainage stack?
- Negative pressure caused by a fast-moving slug of water in the stack
- Pressure that builds below a slug of falling water and can push trap seals into the room (Correct answer)
- Water pressure from the supply system entering the drain
- Pressure loss from undersized vent pipes
Correct answer: Pressure that builds below a slug of falling water and can push trap seals into the room
As a slug of water falls down a tall stack, it compresses air below it, creating positive pressure that can force trap seals out of lower-floor fixture traps.
Question 3: A floor drain trap primer is used to:
- Increase the flow rate through the floor drain
- Periodically supply water to a floor drain trap to prevent the seal from evaporating (Correct answer)
- Prime the sewer ejector pump before use
- Clean the floor drain screen automatically
Correct answer: Periodically supply water to a floor drain trap to prevent the seal from evaporating
Trap primers supply small amounts of water to infrequently used floor drain traps to replace water lost to evaporation and maintain the sewer gas seal.
Question 4: What material is NOT permitted for use as a DWV pipe under the IPC in a concealed location?
- ABS plastic pipe
- Cast iron soil pipe
- PVC schedule 40
- Galvanized steel threaded pipe (Correct answer)
Correct answer: Galvanized steel threaded pipe
Galvanized steel threaded pipe is not listed for DWV use under the IPC; approved materials include cast iron, ABS, PVC, and copper drainage tube.
Question 5: A combination waste and vent system is typically used for:
- Multistory high-rise buildings
- Floor drains and sinks in slab-on-grade commercial kitchens where conventional venting is impractical (Correct answer)
- Outdoor hose bibbs and yard drains
- Water closets in basement bathrooms only
Correct answer: Floor drains and sinks in slab-on-grade commercial kitchens where conventional venting is impractical
Combination waste and vent systems use oversized horizontal drain pipes as both the drain and vent, and are commonly applied to floor drains in slab construction where vertical venting is difficult.
Question 6: When a drain pipe passes through a fire-rated assembly, what is required?
- The pipe must be wrapped in pipe insulation
- A listed fire stop or intumescent collar must be installed to maintain the fire rating (Correct answer)
- The pipe must be upsized one size at the penetration
- No special treatment is required for plastic DWV pipe
Correct answer: A listed fire stop or intumescent collar must be installed to maintain the fire rating
Any drain pipe penetrating a fire-rated floor, ceiling, or wall assembly must be protected with a listed firestop system or intumescent collar to restore the assembly's fire rating.
Question 7: What test is commonly used to check a completed DWV system for leaks before covering it?
- Hydrostatic pressure test at 100 psi
- Air pressure test at 5 psi or water test filled to the highest point (Correct answer)
- Vacuum test at 15 inches Hg
- Dye test using colored water from the supply system
Correct answer: Air pressure test at 5 psi or water test filled to the highest point
DWV systems are tested with either an air test at 5 psi or a water test where the system is filled to the level of the highest stack opening, per IPC Section 312.
